This invention is concerned with the location of radiation sources which are generally known as direction finding systems. The invention is a remote radiation detection system which employs fixed omnidirectional radiation responsive means and relies on measuring the intensity of the received radiation to determine the location and size of radiation sources. This invention is of particular interest for nuclear radiation but is not restricted thereto.
Direction finding systems are known which use different types of radiation and are employed in many applications. Direction finding systems are used to locate any object or source of radiation which is of particular interest. One of the most common applications is in navigation to determine the location of a moving vehicle such as an airplane. Other applications of direction finding are in surveying, astronomy, geology, and medicine.
In navigation systems, many methods have been devised which use directional antennas for direction finding. Time referencing of a signal by measuring the elapsed time interval or phase change are other methods used in navigation systems for direction finding. Similar techniques also exist in applications such as surveying, astronomy, seismic measurements and geological exploration. Generally, these systems are designed to operate at a particular frequency or band of frequencies rather than to operate with an inherently noisy signal whose intensity is the major characteristic. They also become more complex when the detectors have directivity and the detectors must be moved or rotated to scan the field.
In the prior art, nuclear radiation detectors are given directivity by mounting a shield with a window around the detector. Directivity is obtained when the shield is rotated. The addition of a similar detector with a shield rotated about a parallel axis also provides directivity. By triangulation, the source location in two dimensions is determined. To determine the source location in three dimensions, a third detector is required with a shield rotated about a non-parallel axis.
Detectors for nuclear radiation have also been developed with special designs to give them directional characteristics without the use of shielding so that the system is light in weight. The detector is then rotated to provide directivity.
Another light weight detection system of the prior art is to use two detectors on a common mounting separated by some radiation shielding material. When the detectors are rotated so that both face the source, the difference of the two detectors produces a minimum or null signal which gives the direction of the source. In another method, two detectors on a single mounting are used and a radiation shield is placed directly in front of one detector. When the detectors are rotated so that both face the source, a maximum signal is produced from the difference signal of the two detectors.
In the above methods of the prior art, only the radiation intensity of the source is measured. However, in order to obtain directivity, means must be provided to rotate the detector assembly. Location of a source in two dimensions requires two rotating detector assemblies and location of a source in three dimensions requires three rotating detector assemblies.
As will be appreciated by those skilled in the art, it is desirable in nuclear radiation detection systems to have detectors which can be placed in a fixed position instead of being moved about or rotated when operating. When a detector is in a fixed position, the complexity is reduced and the reliability is increased.